Bipolar electrochemical spacer

ABSTRACT

The present invention provides a device capable of reducing the resistance and increasing the ion exchange rate in an electrodialysis, electro-deionization, or capacitive deionization apparatus and a method for producing said device. More specifically, the device is an electrodialysis spacer designed to have an ionically conductive surface of either cationic nature, anionic nature or a combination of both, which act as conductive pathways for ions as they move towards their respective electrode. The method of producing said spacer involves coating a substrate, such as a woven mesh, expanded netting, extruded netting or non-woven material, with perm-selective ionomer solutions and applying that substrate to an inert spacer material that has undergone chemical or mechanical etching.

FIELD OF THE INVENTION

The present invention pertains to a bipolar, ion-conducting spacer and amethod for producing an ion-conducting spacer for use in an ion-exchangewater treatment system, such as electrodialysis (ED), electrodialysisreversal (EDR), electrodialysis metathesis (EDM), reverseelectrodialysis (RED) or electro-deionization (EDI).

BACKGROUND

In the current state of the art, electrodialysis, as a method, is usedto selectively remove positive and negative ions from a water source,such as brackish water or the brine solution produced in reverse osmosisunits, through transportation of salt ions from one solution to anothersolution via ion-exchange membranes upon the application of anelectrical current. The electrodialysis apparatus itself is comprised ofa pair of electrodes, where a voltage is applied to initiate anelectrochemical reaction, alternating anionic and cationic exchangemembranes, which are used to selectively separate ions from one streamwhile concentrating said ions in adjacent streams from a dilute solutionfeed stream (dialysate compartment) to concentrate stream (brinecompartment), and spacer materials, which are placed in between the ionexchange membranes. While the anode attracts negatively charged ions(e.g. chloride) and the cathode attracts positively charged ions (e.g.sodium), it is the primary function of the spacer material to createturbulence in the flow field and to restrict the membranes fromcontacting one another.

Although the spacer does provide a necessary function to theelectrodialysis unit, it doesn't come without a cost. The electricalenergy required to transport ions from one stream to another is afunction of the resistance of the system, via Ohm's law (Eq. 1), where Vis the electrical potential, i is the current density, and R is theresistance. While the rate of desalination may be accelerated through anincrease in the electric potential (V), current density (i) (i.e. theamount of electric current flowing per unit cross-sectional area of amaterial), as a function of electric potential (V), this can beincreased only to a point of electrochemical polarization impedance.Turning to the second, more highly mutable function, the resistance ofthe system, this opposing force can be seen to be impacted largely byboth K, the conductivity of the water in the unit (which consequentlydecreases as the ions are removed and the distance between themembranes), and L, determined by the spacer thickness. Thus, resistancescales linearly (i.e. increases) with the intermembrane spacing, as seenby equation 2.V=i*R  Equation 1R=K ⁻¹ *L  Equation 2

Previous attempts to improve spacer design constructed to overcome theaforementioned infirmities use primarily inert polymeric materials whichare able to create turbulence, resulting in an increased rate of contactof ions with membrane surfaces and subsequent increased ion exchangerates, but do not provide any means of reducing electrical resistance.As evidenced in Herron et. al (U.S. Pat. No. 5,407,553), the inventorsdisclose “an electrocell having a novel design for promoting highturbulence in that portion of the electrocells sensitive to fouling orlimiting current problems” and “membranes (e.g., anode membrane, brinemembranes and cathode membranes) [are] intentionally allowed to deflectin response to fluid pressure differentials so that a flow path with aconstantly changing direction is formed”. Yet the turbulence created bythe invention detailed in the '553 patent suffers from seriouslimitations that (1) requires energy input detracting from the overallefficiency of the process and (2) creates the rate limiting step ofphysical manipulation of salinated water through a dialysis stack.

Additionally, U.S. Pat. No. 6,090,258 issued to Mirsky et al., describesan ion-exchange spacer and processes of making said spacer incorporatingboth heterogeneous and homogeneous ion-conducting coatings. Inparticular, the authors describe a process of coating a polymericnetting with a polymeric coating, where the coating contains ionexchange resin particles to impart ion exchange capacity. Although itdoes reduce the resistance, the described method is limited in that itcould only make a unipolar conductive spacer, consisting of eithercation-conducting or anion-conducting spacer material, thereby greatlydecreasing its utility in water desalination as a unit functioning toremove both positively and negatively charged ions with one bipolarfunctioning spacer substrate.

Some other previous attempts exist which utilize textured membranes forenhanced ion exchange. Various disclosures impart a three-dimensionalshape to the surface of the membranes while also varying the thicknessof the membranes (See generally Pat. Application Nos. WO2005009596A1,WO2002014224A1, and US20170029586A1. So, although this does reduce theresistance, it is limited in that it does not create sufficientturbulence in the fluid flow field or provide for a sufficient decreasein the amount of electrical resistance that is the required to advanceion conduction and electrodialysis beyond current practices.

Thus, there is a long-standing need in the art for an apparatus andmethod of creating a bipolar conductive spacer that maximally reducesthe electrical resistance, via both an anionic and cationic coating, andcreates turbulence sufficient to enhance and advance electrodialysis,electro-deionization, and capacitive deionization beyond its limitedcurrent state. The present invention satisfies this long-standing needin the art and seeks to remedy all the deficiencies detailed above.

SUMMARY

The electrodialysis device described herein illustrates an apparatus andmethod for use exhibiting a mixture of anion and cation ion-exchangematerials adhered to a electrodialysis spacer surface material (that maybe woven porous or non-woven) to produce a network of both anionic andcationic exchange channels that results in a bipolar, ionicallyconductive electrochemical spacer device designed to (1) increasing thesurface area of the substrate (applied mesh or net material) and (2)create an anionic and cationic substrate through application ofsolutions to the surface of the spacer surface material. This increasein surface area directly enhances the creation of turbulent passageways,thereby improving ion-exchange rates via amplified rates of contact withappropriate membranes. Equally, the creation of a dually charged,bipolar ion-conductive spacer surface allows for a greatly acceleratedion exchange rate beyond that of a unipolar ion-conductive surface.

BRIEF DESCRIPTION OF THE DRAWINGS

Refer now to the drawings wherein depicted elements are not necessarilyshown to scale, and like, or similar, elements may be designated by thesame reference numerals through the several figures. In the drawings:

FIG. 1 is a detailed schematic representation of an operatingelectrodialysis apparatus described herein to reduce resistivity of thediluate and concentrate chambers.

FIG. 2 is a general arrangement of an exploded view of the spacersbetween alternating membrane types within an electrodialysis apparatus.

FIG. 3 is a detailed schematic of a bipolar conductive spacer surfaceprepared using a process with anionomer and cationomer solutions appliedsimultaneously to an ion exchanging unit spacer's exterior surface.together with the movement of anions and cations along the surface ofthe spacer in route to the surface of the ion exchange membranes.

FIG. 4 is a representation of the present invention that has an ionicsurface that is the same as the adjacent membrane surface.

FIG. 5 is a flow diagram detailing the process of applying ionomer tothe surface of a spacer material that firsts modifies the surface of thespacer.

FIG. 6 is a flow diagram detailing the process of applying ionomer tothe surface of a spacer material without surface preparation or surfacemodification.

FIG. 7 is a simplified schematic of the process of applying ionomer tothe surface of a spacer's exterior to increase the conductivity of thespacer material.

FIG. 8 is a simplified schematic of a continuous roll-to-roll processfor producing bipolar conductive spacer material.

FIG. 9 is a graph that compares the resistance of an electrodialysisspacer with and without conductive spacers

FIG. 10 a graph that compares the resistance of an electrodialysisspacer with and without conductive spacers

It should be understood, however, that the specific embodiments given inthe drawings and detailed description do not limit the disclosure. Onthe contrary, they provide the foundation for one of ordinary skill todiscern the alternative forms, equivalents, and modifications that areencompassed by the scope of the appended claims.

TERMINOLOGY

Terms used herein will be recognizable to those of ordinary skill in theart. Accordingly, it should be understood that when not explicitlydefined, terms should be interpreted as having the meaning presentlyaccepted by those having ordinary skill in the art.

In this application, the use of the singular includes the plural, suchthat the articles “a” and “an” mean “at least one”, and the use of theconjunction “or” has the inclusive meaning “and/or” unless specificallystated otherwise. Unless otherwise specified, the term “including” (aswell as its other forms, such as “includes” and “included”) isopen-ended and not intended to be limited to any specifically identifieditems. Unless otherwise stated, terms such as “element” or “component”encompass not just unitary modules, but also multi-module assemblies orsubmodules providing the same characteristics. As used herein, the terms“comprising,” “having,” and “including” are synonymous, unless thecontext dictates otherwise.

DETAILED DESCRIPTION

Advantages of the present invention will become readily apparent tothose skilled in the art from the following detailed description,wherein there are described certain preferred embodiments of theinvention and examples for illustrative purposes. Although the followingdetailed description contains many specific details for the purposes ofillustration, one of ordinary skill in the art will appreciate that manyvariations and alterations to the following details are within the scopeof the invention. Accordingly, the following embodiments of theinvention are set forth without any loss of generality to, and withoutimposing limitations upon, the claimed invention. While embodiments aredescribed in connection with the description herein, there is no intentto limit the scope to the embodiments disclosed herein. On the contrary,the intent is to cover all alternatives, modifications, and equivalents.

The present invention provides a device capable of reducing theresistance in an electrodialysis, electro-deionization, or capacitivedeionization apparatus and a method for producing said device. Morespecifically, the device is an electrodialysis spacer to be used togreatly enhance ion-exchange rates which is designed to have anionically conductive surface, of either cationic nature, anionic natureor a combination of both, which acts as conductive pathways for ions asthey move towards their respective electrode—negatively charged ions(e.g. chloride) toward the positively charged anode and positivelycharged species (e.g., sodium) toward the negatively charged cathode.Furthermore, the invention pertains to an electrodialysis,electro-deionization or capacitive deionization apparatus that utilizesa spacer material having an ionically conductive surface.

The invention also pertains to the process and method of producing theionically charged, ionically conductive spacer wherein thecharge-neutral spacer displays an ion-conducting woven mesh or netmaterial. The process involves coating a substrate, such as a wovenmesh, expanded netting, extruded netting or non-woven material, withperm-selective ionomer solutions (ionomer solutions being thesolubilized form of an ion exchange resin or membrane). The ionomersolution is applied to the non-conducting spacer via a coating process,such as, but not limited to, spray-coating, inkjet printing, curtaincoating or dip-coating. The coated spacer is then cured to adhere theion-conducting material to the non-conducting substrate and to removesupporting surfactants from the spacer surface. Prior to coating thesubstrate surface an additional step may be taken to increase thesurface area of the substrate through chemical or mechanical processesincluding but not limited to acid etching, sandblasting, laser etchingfor enhanced turbulent effect.

In a preferred embodiment, the conductive spacer is a coated mesh orextruded netting 110 and 111 used to separate membranes 105, 106, and107 in an electrodialysis device as shown in FIG. 1. An electrodialysisapparatus comprises an anode 103 and a cathode 104 encompassing a seriesof fluid channels 101, 112, 113 and 102. The fluid channels areseparated by ion exchange membranes 105, 106 and 107. The ion exchangemembranes alternate between anionic exchange membranes 105 and 107 andcationic exchange membrane 106. Anionic exchange membranespreferentially allow the passage of negatively charged ions 108 andsubstantially block the passage of positively charged ions 109. Cationicexchange membranes preferentially allow the passage of positivelycharged ions 109 and substantially block the passage of negativelycharged ions 108. The fluid channels 101 and 102 contain the electrolytethat is in direct contact with the anode 103 and cathode 104, which maybe the same or different fluid as the fluid entering the electrodialysisapparatus 100.

In an electrodialysis cell, when an electric charge is applied to theanode 103 and cathode 104, the ions in the fluid stream 100 flow throughchannels 110 and 111 migrate towards the electrode of opposite charge.The alternating arrangement of the ion exchange membranes thus producesalternating channels of decreasing ionic concentration 112 andincreasing ionic concentration 113. The number of channels 112 and 113may be increased through the addition of more alternating pairs ofmembranes to increase the capacity of the electrodialysis apparatus.Further, the functioning ability of an individual electrodialysis cellmay be greatly augmented by configuring electrodialysis cells intoelectrodialysis stacks (i.e. a series of multiple electrodialysiscells).

To create the fluid channels 112 and 113, spacers are inserted betweenthe membranes. This spacer may be comprised of two parts as shown inFIG. 2. The first part is a spacer frame 210 and 211 which can be madeof a plastic or elastomeric material and act as a seal between fluidchambers as well as providing a seal between the internal fluids and theoutside. The second part is a spacer mesh 205 and 207, which can beeither woven or extruded netting 205 and 207 that spans the internalopening in the sealing frame 210 and 211 and provide fluid channelsbetween membranes 203 and 206, and 206 and 209. The spacer mesh 205 and207 and spacer frame 210 and 211 can optionally be connected to formspacer 204 and 208, through methods including but not limited to sonicwelding, lamination or adhesives. By alternating the orientation of thespacer 204 and 208 two distinct channels 201 and 202 are formedinternally between anionic exchange membrane 203 and 209 and cationicexchange membrane 206.

A primary source of electrical resistance in the electrodialysisapparatus is due to fluid in channel 112 (see FIG. 1) as it reduces inionic concentration. The present invention addresses this issue throughthe application of ionomers to the surface of the mesh spacer thatseparates the membranes. In an exemplary embodiment, the ionomers areapplied concurrently resulting in a surface with bipolar ionicconductivity, exhibiting both cationic and anionic qualities, as shownin FIG. 3. The concurrent coating of the mesh substrate 301 produces asurface partially coated in anionic exchange ionomer 302 and partiallycoated in cationic exchange ionomer 303 (see FIG. 3). The result is anetwork of oppositely charged ionic pathways, which may be lessresistive to ionic flux than the surrounding fluid. Functionally, asdepicted in FIG. 3, as the ionic solution passes through the electricfield in the electrodialysis apparatus, transport is facilitated byionic pathways to the surface of the adjacent ion exchange membranes 308and 309. The anionic coated surfaces 302 have positively chargedfunctional groups 306 which transport negative anions 305 to the anionicmembrane 308. Positive cations 304 are repelled by the positivelycharged functional groups 306 on the anionic coated surface 302.Conversely, the cationic coated surface 303 contains negatively chargedfunctional groups 307 that attract and transport positive cations 304 tothe cation exchange membrane 309 and negative anions 305 are repelled bynegative functional groups 307.

In another exemplary embodiment, a mesh spacer 401 is coated withcationic exchange ionomer 407 on one side and with anionic exchangeionomer 408 on the other side as shown in FIG. 4. This coating methodextends the ion exchange material into the flow paths away from thesurface of the ion exchange membranes, which lowers the resistance ofthe flow channels. Here, the cationic exchange membrane 404 is extendedby the cationic coated surface 402 and the anionic exchange membrane 406is extended by the anionic exchange surface 403.

Representationally, FIG. 5 provides a flow diagram illustrating theprocess of producing the ion-conductive spacer that is the presentinvention. The first step is the surface preparation. Here a chosenmaterial, such as Nylon, PET, PTFE, or any other plastic, isappropriately shaped to allow fluid (e.g. water) to flow both around andthrough it. This process could also include cutting the spacer to thedesired size for incorporation into an electrochemical apparatus (e.g.an electrodialysis apparatus). This sizing step could also be done at adifferent point in the process, such as just prior to incorporation intoa device.

The second step in the process is surface modification. In this step,the spacer material is modified to enable greater adhesion between theinert plastic substrate and the ionic coating. The general idea is toincrease the surface energy of the substrate, which can be accomplishedvia both physical and chemical methods. Physical methods include, butare not limited to, flame oxidation, corona discharge plasma, laseretching, hollow cathode glow discharge, and sandblasting. Chemicalprocesses to increase the surface energy include, but are not limitedto, treatment with strong acids (chromic, nitric, etc.), peroxideattack, and etching with strong bases (e.g. sodium hydroxide, potassiumhydroxide, etc.).

Following surface modification, the surface is cleaned. The cleaningprocess includes rinsing the surface alternatingly with light alcohols(ethanol, 2-propanol, etc.) and deionized water. The cleaned surface isthen dried and is ready for the application of the ionic material.

The application process is a coating process, and therefore can be donevia such methods as dip-coating, spray-coating, roll-coating, etc. In apreferred embodiment, spray-coating is used. Here, a dilute solutioncontaining solubilized ionomer is entrained in an airstream. Thecombined stream passes through an atomizing nozzle and is applied to thespacer surface. Either the nozzle, the spacer, or both are moved suchthat the entire exposed surface of the spacer is coated with thesolution. The process variables (i.e. solution concentration, number ofpasses, flow rate, droplet size, etc.) will all have an impact on theloading of the produced spacer material.

The drying process serves to remove excess solvent and to cure (set) theionomer into a resin. The drying process can be done concurrent with,and/or subsequent to, the coating process. The drying process can bedone with, or without, the addition of heat source. Heat can betransferred to the spacer via convection, radiation, or conduction, withthe preferred method being convection.

The next step in the process is to immerse the coated spacer intosalt-containing water (e.g. a mixture containing a combination of sodiumchloride and water. This immersion step allows for the ionomer toexchange its pendant charge group (such as hydroxide) for a salt ion,such as chloride.

The final step in the process is to incorporate the ion conductivespacer into the electrochemical device (e.g. an electrochemical ionseparation device). The spacer must be sized to fit within the activearea of the device, and preferably out of the sealing area. The spacercan be sized prior to coating, after coating, or at another step withinthe process. Depending on the orientation of the ionic coating, it maybe important which side needs to face which membrane. In one preferredembodiment, a spacer with different ionic coatings on each side of thespacer is placed such that the anionomer-coated surface faces the anionexchange membrane, and the cationomer-coated surface faces the cationexchange membrane within the stack as in FIG. 4.

A conductive spacer may also be produced via a process with no surfacepreparation or surface modification. The description of the final foursteps of FIG. 5 detail how such a process would work.

Another preferred embodiment incorporates a spray-coating process forapplying ionic material. Atomizing spray nozzles 701 and 702 distributeionomeric solution where pressurized air entrains the solubilized ionicmaterial onto a receiving surface. The tip of the nozzle atomizes fluidinto microdroplets, 703 and 704, which are deposited onto the spacersurface 705. In some embodiments, microdroplets 703 and 704 contain thesame ionomer solution, either cationic or anionic, and in otherembodiments microdroplets 703 contain an anionic ionomer solution, whilemicrodroplets 704 contain a cationic ionomer solution. Items air 706 andfan 707 illustrate the convective drying process wherein air 706 ismoved by a fan 707 onto the spacer surface. The fan 707 can also containa heating element such that the air 706 transfers heat to aid in thedrying process.

In a yet another embodiment, bulk spacer material is wound onto adispensing roll 801, fed through rollers to an area where it is exposedon either side to spray ionomeric solution distributing nozzles 802 and803. Ionomeric solution distributing nozzles 802 and 803 may contain thesame ionomer solution (either anionic or cationic), or ionomericsolution, distributing nozzle 802 may eject either cationic or anionicionomeric solution, and ionomeric solution distributing nozzle 803 mayeject either cationic or anionic ionomeric solution. Alternatively, theprocess herewith defined may consist of any combination, in parallel,series or alternating combination that results in the uniform,patterned, regular or irregular application of the ionomeric solution.Fans 804 and 805 may or may not contain heating elements to provideconvective heat transfer to dry the spacer material. Convection bothspeeds up the drying process and helps to reduce the amount of materialblocking the open areas of the spacer. Receiving roll 806 shows thefinished material that may undergo further processing.

EXAMPLES Example 1

Nylon mesh spacer was cut to the desired dimension for use in a flowingelectrodialysis apparatus. Solutions of solubilized Nafion and ananionic ionomer (FUMION FLA from Fumatech Gmbh) were diluted to 1 wt %using reagent alcohol (blend of ethanol, methanol and 2-propanol). Theseparate solutions were loaded into separate air-driven spray guns. Thespacer was held such that one side was exposed to the spray gun. First,the exposed side was sprayed with the Nafion solution, covering allavailable surfaces. The wet spacer is subsequently dried using a heatgun (a heating coil with fan and a nozzle for directing the heat). Thisprocess was repeated until the desired loading of 1.25 mg/in² wasapplied to the first side. The coated spacer is then reversed, exposingthe uncoated side to the spray gun. Then, the entire process wasrepeated with the anionic solution.

Six of these spacers were incorporated into a flowing electrodialysisapparatus. The coated spacers were placed in between the alternatinganion and cation exchange membranes. Care was taken to place theanionic-coated side of the spacer facing the anion exchange membrane andthe cationic-coated side facing the cation exchange membrane. Brackishwater was desalinated using this device and the performance was comparedto a standard design where the only difference is that the spacers werenot coated with the ionomer solutions. As seen in FIG. 9, the resistanceof the system with the conductive spacers is lower than the baselinecell device with non-conducting spacers at all salinities, and thisdifference becomes greater as the total resistivity of the systemincreases (i.e. at low salinity values). In the experiment the salinitywas reduced two orders of magnitude from the initial concentration.

Example 2

Solutions of anionic and cationic ionomer at 1 wt % were made in the waydescribed in Example 1. Instead of spraying each solution on one side ofthe spacer, here the two solutions are sprayed simultaneously onto theNylon spacer. The two solutions are sprayed, and the wet spacers dried,as described above, until the desired loading of 1.25 mg/in2 isachieved. Afterward the spacer is reversed, and the process repeateduntil the reverse side also reaches the desired loading. Spacers made inthis manner can be placed between the alternating ion exchange membranesof the electrodialysis apparatus in either orientation without affectingthe performance.

Six of these spacers were incorporated into an electrodialysisapparatus, placed in between alternating ion exchange membranes.Brackish water was desalinated using this device and the performance wascompared to a standard design where the only difference is that thespacers were not coated with the ionomer solutions. As seen in FIG. 10,the resistance of the experimental design is similar to the controldesign (identical electrodialysis apparatus with non-conducting spacers)at the initial concentration. As salt is removed from the product waterin the electrodialysis process, the experimental design becomes lessresistive relative to the control, and this difference increases as moresalt is removed from the system. In this experiment, the salinity wasreduced 1.5 orders of magnitude from the initial concentration.

What is claimed is:
 1. An electro-chemical apparatus for reducing theresistance in an electrodialysis, electro deionization, or capacitivedevice, comprising: a. a pair of electrodes; b. an applied voltage; c.alternating anionic and cationic exchange membranes placed between thepair of electrodes for separation of ions from a depleted stream to aconcentrate stream; d. an ionically neutral, non-conducting spacer whichmay be woven, porous or non-woven; e. said spacer with an exteriorsurface having a first side and a second side opposite the first side,the first side comprises a first coating comprising a cationic exchangeionomer and the second side comprises a second coating comprising ananionic exchange ionomer, wherein the first coating is different fromthe second coating.
 2. The electrochemical apparatus of claim 1, whereinthe first and second coatings are a topical application onto theexterior surface of said ionically neutral, non-conductive spacer thatis a woven mesh, expanded netting, extruded netting or a non-wovenmaterial.
 3. The electrochemical apparatus of claim 1, wherein the firstand second coatings are applied to said spacer via a coating processcomprising spray-coating, inkjet printing, curtain coating ordip-coating.
 4. The electrochemical apparatus of claim 3, wherein thecoated spacer is cured to assure adherence of ion-conducting, ionicallycharged material to said spacer.
 5. The electrochemical apparatus ofclaim 1, wherein the first and second coatings form a network of anionicor cationic exchange channels, which act as an array of conductivepathways for ions and ion exchange.
 6. The electrochemical apparatus ofclaim 1, wherein said spacer's surface is chemically altered via acidetching treatment with strong, peroxide attack, and etching with strongbases to create deformities in said spacer's surface for the creation ofturbulent rheologic disturbances for an enhanced ion-exchange rate. 7.The electrochemical apparatus of claim 1, wherein said spacer's surfaceis mechanically altered via flame oxidation, corona discharge plasma,laser etching, hollow cathode glow discharge, or sand-blasting for thecreation of turbulent rheologic disturbances for an enhanced ionexchange rate.
 8. The electrochemical apparatus comprising: a. a spacerfor reducing the resistance in an electrodialysis, electro-deionization,or capacitive device where the spacer has a first side and a second sideopposite the first side, the first side comprises a first coatingcomprising a cationic exchange ionomer and the second side comprises asecond coating comprising an anionic exchange ionomer, wherein the firstcoating is different from the second coating, residing between anionicand cationic ion exchange membranes, which facilitates transport of nionic solution through oppositely charged ionic pathways to surfaces ofthe ion exchange membranes; b. at least one anode or a plurality ofanodes; c. at least one cathode or a plurality of cathodes; d. one or aplurality of fluid channels separated by anionic and cationic ionexchange membranes, where the anionic exchange membranes preferentiallyallow the passage of negatively charged ions and substantially block thepassage of positively charged ions and cationic exchange membranespreferentially allow the passage of positively charged ions andsubstantially block the passage of negatively charged ions and exhibitalternating pathways of ever decreasing ionic concentration streams andincreasing ionic concentration streams; e. electrolyte containing fluidchannels in direct contact with the anode and cathode which may be thesame or different fluid as the fluid entering the electrodialysisdevice; and f. an electric charge applied to the anode and cathodethereby causing the ions in the fluid stream to flow through the fluidchannels and migrate toward the electrodes displaying the oppositeelectric charge.
 9. The electrochemical apparatus of claim 8, whereinthe first and second coatings extend the ion exchange material into theflow paths away from the surface of the ion exchange membranes therebylowering the resistance within the flow channels.
 10. Theelectrochemical apparatus of claim 8, wherein the spacer residingbetween ionically charged membranes comprises: (1) a spacer frame thatacts as a seal between fluid chambers and as a seal between internalfluids and the exterior; and (2) a spacer mesh, which is either woven orextruded netting, that spans the internal opening in the sealing frameand provides fluid channels between ionically charge membranes throughalternating fluid pathways through said spacer and into contact withsaid ionically charged membranes.
 11. The electrochemical apparatus ofclaim 9, wherein the spacer is made of a non-reactive, non-ionic plasticor elastomeric material that is made to display ionomers resulting in aspacer that is bipolar in nature.